In general, an air compressor is made up of an electric motor which is driven to rotate by electric power supplied thereto, an air compressor which is driven by the electric motor to compress air sucked thereinto from the outside and discharge the compressed air and an air tank for storing the compressed air which is discharged from the compressor. JP-A-2000-283046 discloses an air compressor in which the supply of electric power to an electric motor which drives a compressor is implemented by an inverter control unit which functions to reduce consumed electric by driving the electric motor efficiently by detecting the rotational position of a rotor of the electric motor and controlling the supply of current and voltage to a coil of a stator of the electric motor by varying frequencies thereof according to detection outputs.
The inverter control unit is made up of an electric power supply module which is made up, in turn, of a semiconductor switching element for switching current and voltage supplied to the stator coil of the electric motor and other constituent components and a control module for controlling the electric power supply module based on detection signals of the rotational position of the rotor inside the electric motor. Since the semiconductor switching element making up the power supply module generates heat during its operation, the inverter control unit which includes the electric power supply module on which the semiconductor switching element is mounted and the control module is broken by virtue of heat generated by the semiconductor switching element, and this may lead to a problem that the control of the electric motor is disabled. In general, a protection circuit is formed on the circuit for cutting off the circuit to prevent the failure of the components when the temperatures of the components reach a predetermined temperature. In the air compressor, in the event that the compressing operation is stopped every time the protection circuit works, the operability is deteriorated. To cope with this, in an air compressor which utilizes an inverter control unit like this, it is necessary to cool, in particular, the semiconductor switching element of the electric power supply module in order to prevent the overheat of the inverter control circuit.
In order to facilitate the cooling of the semiconductor switching element itself, the semiconductor switching element of the electric power supply module is formed as an independent inverter module. In the air compressor which utilizes the inverter control unit disclosed in JP-A-2000-283046, this inverter module is separated from the electric power supply module so as to be mounted on a radiator plate, and the radiator plate on which the inverter module is mounted is provided between a pair of air tanks and on a lower side of the electric motor, so as to cool the inverter module by a flow of air that is generated by cooling fans mounted at both ends of the rotating shaft of the electric motor in order to cool the electric motor and the compressor.
In the air compressor disclosed in JP-A-2000-283046, the radiator plate on which the inverter module, which is the heat generating component, is mounted is disposed between the pair of air tanks, so as to cool the inverter module via the radiator plate by cooling air which cools the compressor and the electric motor. In order to cool the inverter module properly, it is necessary to prepare a radiator plate having a wide surface area, and it is also necessary to secure a space for installation of the radiator plate, and therefore, this configuration has constituted a cause for preventing the attempt to make the air compressor small in size and light in weight.
In addition, in the air compressor disclosed in JP-A-2000-283046, a circuit board of the electric power supply module which is made up of the other components excluding the inverter module, which is the heat generating component in an inverter circuit, is separated from the inverter module and is disposed between and below the pair of air tanks with its face turned up. In the event that the circuit board of the electric power supply module and the inverter module are disposed separately from each other in this way, wirings including an electric power supply wire, a signal wire and the like need to be provided therebetween, and this serves to increase the production cost of the substrates and manhours required in assembly of the compressor, leading to a problem that the production cost of the compressor is increased.